It is frequently desirable to incorporate into toothpaste formulations certain molecules which may often be air sensitive, for example vitamin C. Often the degradation products produced on exposure of the toothpaste formulation to air are a different colour to the original compound; in the case of vitamin C its air decomposition products are coloured brown. Hence it has been a major disincentive to manufacturers who would wish to incorporate such air sensitive compounds in toothpaste formulations that such pastes tend to discolour after a period of time, thereby appearing visually unattractive to a potential user. Similar problems may occur with other air sensitive substances such as certain flavour molecules or pharmaceuticals, which upon air-induced degradation result in impairment or even loss of the respective desired properties of the toothpaste.
Such problems have been partially overcome by the use of air impermeable tubes. Traditional tubes such as those made from metals such as aluminium are regarded by consumers as old fashioned, and also these tubes are not ideal from other perspectives, as they tend to crack after extended use, thereby causing the toothpaste to leak. Paint on the surfaces of these tubes also tends to crack and flake off upon extended use.
Plastics tubes now enjoy popularity. However, these also have disadvantages, since they are prone to the permeation of air through the tube and into the contents, and also the permeation of volatile substances in the paste out of the tube, with the result that the toothpaste shows a tendency to discolour and/or lose flavour or other active properties on storage. Air impermeable plastics tubes have been developed to overcome these problems, and have in general been successful in preventing air gaining access to the toothpaste. Such solutions to these problems are not without their own problems though; an air impermeable tube costs typically 3-10 times the amount of an ordinary plastic tube.
Laminated tubes, for example tubes containing a metal layer such as aluminium laminated between two layers of a plastics material such as polyethylene, have also been developed which in practice have most of the advantages of both plastic and metal tubes. Such tubes are effectively air impermeable, and are the generally preferred choice of manufacturers in which to pack toothpaste for commercial sale.
However, because of technical problems associated with the assembly of such tubes, complete tubes made entirely of laminated material have not been available. In practice, sleeves of laminated tube material are heat sealed to a preformed plastics collar nozzle assembly which is sealed by a plastics cap. Toothpaste is then dosed into the other open end, which is then crimped or otherwise sealed. The toothpaste can then be dispensed through the preformed nozzle.
Overall it has not been possible to totally prevent toothpaste contained in tubes from coming into contact with air. Where this is caused by the ingress of air on prolonged storage, it is observed that most of this ingress occurs through the collar of the tube; the toothpaste is also exposed to the small amount of air that typically remains in the nozzle area of the tube after it has been filled. The problem is exaggerated if the filling of the tube does not occur uniformly, as is bound to happen occasionally in the mass manufacture of packaged toothpaste. In such circumstances, small unwanted air voids will be trapped in the toothpaste, usually adjacent the collar/nozzle assembly, after filling. This is still a general problem for toothpaste manufacturers since it can lead to dehydration, discolouration and flavour loss from the paste, in particular in parts of the tube near the collar. The problem is particularly acute for the manufacturer of toothpaste who wishes to include air sensitive compounds in a toothpaste formulation, such as for example vitamin C. It is found that after storage such vitamin C containing toothpaste formulations discolour in the vicinity of the tube collar; hence the first few centimeters of the toothpaste that are dispensed are discoloured. Such a product is obviously quality suspicious to the consumer, if for example the bulk of the toothpaste is coloured white but the first few centimeters are coloured brown.
It has also been observed that even if formulations containing air sensitive compounds such as vitamin C are stored in special tubes which have been made air impermeable, the surface of the paste which is in contact with the air contained in the aforementioned nozzle gap rapidly turns brown. Hence, even the provision of totally air impermeable tubes would not totally solve the problem, whilst using current technology the most cost effective toothpaste packaging is not totally air impermeable.
Hence there exists a need for a method of packaging toothpaste which contains air sensitive components which prevents the discolouration or other form of degradation of such toothpaste caused by exposure of areas of the toothpaste to air. The problem is noticeable even when air impermeable packaging is used, but is particularly noticeable when the packaging used is not totally air impermeable, for example if an effectively air impermeable laminated toothpaste tube is fitted with an air permeable (e.g. polyethylene) collar.
It is known in the art to provide different reactive components of a toothpaste composition which are to be reacted together in use in separate compartments of a toothpaste package, which two components are brought into contact with each other for reaction together at the time of dispensation from the package. Examples of such known systems are described in GB-A-1561418 and GB-A-2112642. These systems however do not address the problem of air-induced degradation of either of the reactive components, or indeed other components of the toothpaste composition.